Glass fibres and compositions containing glass fibres

ABSTRACT

Fibre reinforced cementitious products are described comprising glass fibrous material distributed throughout a cement matrix, in which the glass is one having per se a degree of alkali resistance such that when tested in the form of an abraded fibre of length 2 1/2 inches and diameter of from 0.4 to 1.0 X 10 3 inches said fibre has a tensile strength of at least 100,000 p.s.i. after treatment with saturated aqueous Ca(OH)2 solution at 100*C. for 4 hours followed by successive washings at ambient temperature with water, then with aqueous hydrochloric acid (1%) for 1 minute, water, acetone, following by drying, said fibre experiencing not more than 10% reduction in diameter during said test. The reinforcement of Portland cement structures by fibres of diameter 0.4 to 1.0 X 10 3 and lengths of up to 4 inches is described. Alkali resistant glasses useful for production of these products comprise the CaO-MgO-Al2O3-SiO2 glasses including those in the anorthite field, silica zirconia glasses, and silica stannic oxide glasses. The products have outstanding durability and impact resistance.

United States Patent [191 Majumdar Aug. 26, 1975 1 1 GLASS FIBRES AND COMPOSITIONS CONTAINING GLASS FIBRES Amalendu Jyoti Majumdar, Watford, England [75] Inventor:

[73] Assignee: National Research Development Corporation, London, England 22 Filed: Feb. 12,1973

211 Appl. No.: 331,583

Related US. Application Data [60] Division of Ser. No. 127,361, March 23, 1971, Pat. No. 3,783,092, which is a continuation-in-part of Ser. No. 649,463, June 28, 1967, abandoned, and a continuationdn-part of Ser. No. 748,645, July 30, 1968, abandoned, and a continuation-in-part of Ser. No. 31,184, March 26, 1970, abandoned.

[30] Foreign Application Priority Data July 11, 1966 United Kingdom 31025166 Feb. 2, 1967 United Kingdom... 5070/67 Aug. 4, 1967 United Kingdom 35901/67 Apr. 3, 1969 United Kingdom 17448/69 [52] [1.5. CI. 106/50; 106/52 [51] Int. Cl C03c 13/00; C036 3/04 [58] Field of Search 106/50, 52, 54

l 56] References Cited UNITED STATES PATENTS 2,566,134 8/1951 Mockrin et a1. 106/52 2,640,784 6/1953 Tiede 106/50 3,007,806 11/1961 Hartwig 106/50 3,485,702 12/1969 Mochcl 106/52 X FOREIGN PATENTS OR APPLICATIONS 727,779 11/1942 Germany 106/50 147,297 10/1962 U.S.S.R 106/52 1,544,960 9/1968 France 106/52 7,01 1,037 2/1971 Netherlands. 106/50 270,215 8/1970 U.S.S.R 106/52 249,577 12/1969 USSR 106/50 68-4898 1/1969 South Africa 1,243,793 8/1971 United Kingdom OTHER PUBLICATIONS Kozmin, M. 1., Glass & Ceramics, Vol. 17, (1960-1961), pp. 561-563, Continuous Process for Melting & Conditioning High Zircon Glass", Nov. 1960.

Primary ExaminerWinston A. Douglas Assistant Examiner-Mark Bell Attorney, Agent, or Firm-Flynn & Frishauf [57] ABSTRACT Fibre reinforced cementitious products are described comprising glass fibrous material distributed throughout a cement matrix, in which the glass is one having per se a degree of alkali resistance such that when tested in the form of an abraded fibre of length 2% inches and diameter of from 0.4 to 1.0 X 10 inches said fibre has a tensile strength of at least 100,000 p.s.i. after treatment with saturated aqueous Ca( OH) solution at 100C. for 4 hours followed by successive washings at ambient temperature with water, then with aqueous hydrochloric acid (1%) for 1 minute, water, acetone, following by drying, said fibre experiencing not more than 10% reduction in diameter during said test.

The reinforcement of Portland cement structures by fibres of diameter 0.4 to 1.0 X 10 and lengths of up to 4 inches is described.

Alkali resistant glasses useful for production of these products comprise the CaOMgOAl O SiO glasses including those in the anorthite field, silica zirconia glasses, and silica stannic oxide glasses.

The products have outstanding durability and impact resistance.

6 Claims, No Drawings GLASS FIBRES AND COMPOSITIONS CONTAINING GLASS FIBRES This application is a division of application Ser. No, 127,361, filed Mar. 23, 1971 (and now US. Pat. No. 3,783,092), which is a continuation-in-part of applica tion Ser. No. 649,463 filed June 28. 1967, and of application Scr. No. 748,645 filed July 30, 1968. and of application Ser. No. 31,184 filed Mar. 26, 1970. Said application Ser. Nos. 649,463; 748,645; and 31,184 have been abandoned.

This invention relates to reinforced ccmentitious products, e.g. concrete, based on Portland cement or other cement eg. aluminous or so-called highalumina" cement, or mixtures ofthese with other mate rials including blast-furnace slag and pozzolona.

Extensive use has been made, over many years, of as bestos as a fibrous reinforcing material in ccmentitious products employed in the building industry, such as asbestos-cement pipes and roofing sheets. Although used on a large scale, asbestos-cement products are not en tirely suitable for many applications but no acceptable substitute for asbestos has yet been found. Such ce ment-asbestos products are described by Kozacik in US. Pat. No. 3,354,031, wherein asbestos serves as a reinforcement and a very small amount of a mineral glass fibre is included to serve as a filtration aid in producing the products. With the development of glass fibre materials, proposals have been made to substitute glass fibres for asbestos in typical structural and other components but these proposals have in general failed to lead to products of acceptable strength and durability. One approach to increase the strength of cementitious products with glass fibres is described in U.S. Pat. No. 2,793,130. The glass fibres are provided, before incorporation in a cement slurry, with a water-insoluble coating. The coating, designed to improve bonding of glass fibre and ccmentitious materials, is formed by reaction of a polyvalcnt metal salt and a water soluble oxide or hydroxide. However, the principal reason for the lack of success of previous proposals is that the strongly alkaline environment, especially in products based on Portland cement, is sufficiently severe in certain cases to disintegrate glass fibres and for this reason it has been assumed that such fibres cannot be applied successfully as reinforcing materials without resort to protective measures which add considerably to the cost of production of the composite materials. It is found, for example, that protective coatings are insufficiently reliable because in practice it is almost impossible to avoid discontinuities in the coating with the result that the underlying fibre is exposed to a considerable extent to the corrosive action of the cement.

Among the properties of certain glass compositions, a degree of resistance to alkaline solutions has been observed in tests carried out with bulk specimens of glass. These observations, however, have not been recognised as having any bearing on the problem of producing satisfactory cement/glass composite structures in which the glass, being in fibre form, is thereby exposed to the corrosive environment over a considerably large surface area per unit weight.

It has now been found that glass fibre reinforced cement products having outstanding properties can in fact be obtained provided that the glass in fibre form has sufficient alkali resistance to meet the requirements of a test which will be specified hereinafter. It is noted that alkali resistance of the glass fibres is essential for the glass reinforced ccmentitious products of this in vention. This is to be contrasted with prior descriptions of glass fibres exhibiting corrosion resistance to atmospheric conditions, which are generally acidic. One such description is given in U.S. Pat, No. 3.095.311 wherein glasses are shown to resist the action of hydrochloric acid.

In my co-pending application Ser. Nos. 649,463 and 748,645, I have described composite fibre/cementitious products in which the fibrous reinforcing material is primarily a glass having per se a degree of alkali resis tance such that when tested in the form of an abraded fibre of length 2 /2 inch and diameter of from 0.4 to 1.0 X 10 inches said fibre has a tensile strength of at least 100,000 p.s.i. after treatment with saturated aqueous Ca (OH solution at C for 4 hours followed by successive washings at ambient temperature with water, then with aqueous hydrochloric acid (I fl for 1 minute, water, acetone, followed by drying, said fibre experiencing not more than 10% reduction in diameter during said test. Preferably the tensile strength of such fibres after the specified treatment is at least 200,000 p.s.i.

In the case ofproducts based on Portland cement excellent reinforcement is provided by means of fibres having a diameter of about 0.4 to about 1.0 X 10* inches. In practice it is particularly convenient to employ short fibres of length up to about 4 inches, for example, fibres having a length of the order of2.5 inches Glass fibre-reinforced concrete and other cementi tious materials produced in accordance with this invention have been found to exhibit such high strengths that for certain applications the glass fibres may be used in either partial or complete replacement ofstcel in structural components.

It will be appreciated that suitable glass compositions for use in accordance with this invention may be detcrmined by forming fibres therefrom and subjecting such fibres to the test described above.

For reinforcing ccmentitious matrices at temperatures higher than ambient it is desirable, moreover, that the fibres exhibit resistance to attack by alkali metal hydroxides, in addition to attack by Ca (OH A test for this resistance, similar to the previously mentioned test for attack by Ca (OH is as follows:

An individual glass fibre having a diameter in the range of from 0.4 1.0 X 10 inches and a length of 2 inches is exposed to attack by N NaOH solution for 1 hours at 100C. After exposure, the fibre is taken out of the solution at room temperature, washed three times with distilled water, then with dilute HCl (1%) for h minute, followed by several washes with distilled water, Finally, the fibre is washed with acetone twice and dried, after which its tensile strength is determined by measuring the breaking load with an lnstron testing machine and estimating the fibre diameter by an optical microscope.

A glass fibre exhibiting a tensile strength of at least 100,000 and preferably at least 200,000 lbs/sq. in. after the test, and experiencing during the test a reduction in diameter no greater than 10%, has the required properties for reinforcing the ccmentitious matrices at higher than ambient temperatures.

ln assessing the suitability of glass fibres for reinforcing ccmentitious matrices, it is also instructive to study the behavior of the fibres in a cement effluent solution at different temperatures and different ages. The exact Alkali Concentration. in g/litrc NaOH 0.88 KOH 3.45 Cu IOH); 0.48

The desired alkali resistance properties are exhibited by fibres of certain glasses of CaOAI- O;,M- gOSiO type. wherein the oxide ratios are selected so that the composition of the glass lies within the anorthite primary phase volume of the CaOAl. O Si- O MgO phase diagram or in its immediate vicinity. and the glasses are substantially boron free i.e. have virtually no B Such phase diagram is described in the article Ouaternary slags CaOMgOAl O -SiO-,: initial crystallization and fields of crystallization at constant magnesia planes by G. Cavalier and M. Sandrea-Deudon. Revue de Metallurgie. S7. l143l 157 (December 1960).

Within this group of glasses one preferred class of glasses is represented by those in which the main oxide percentages are selected to be the following ranges:

Minor amounts of other metallic oxides such as also impart alkali-resistance may be present also, for example, TiO- Cr Q- ZrO F0 0 ZnO, BaO and MnO. The total amount of these additives will normally be less than [0% by weight ofthe overall oxide mix of the glass.

For locating the compositions of the more complex glasses in the CaOAl O SiO -MgO phase diagram, it may be assumed that optional substituent ZrO substitutes for SiO optional substituents TiO Fe O Cr O for A1 0 and optional substituents BaO. MnO. ZnO for CaO.

The optional substituents. if their percentages are high, may sometimes change the composition of the glass in such a way that it falls outside the anorthitc primary phase volume of the CaO-Al ,O;,-MgOSiO- system but still exhibit adequate alkalbresistance. An example of such a glass is one containing a relatively high total percentage of MgO MnO. say up to 207:.

The present invention comprises a composite fibre/- cementitious product in which the fibrous reinforcing material is at least partly and preferably primarily or wholly glass fibrous material. the glass having sufficient 4 alkali resistance per se to pass the test hereinbefore specified. said fibrous material being distributed throughout a cement matrix.

The present invention also provides a process for producing a reinforced cementitious product comprising incorporating into the raw cementitious mix prior to setting glass fibrous material. the glass having alkaliresistance sufficient to pass the above-mentioned test.

It will be appreciated that the glass fibre tested should be initially in an abraded state as opposed to the virgin" state in which it is originally made at the point of actual manufacture by pulling. extrusion or the like. The "virgin'- condition of a glass fibre is rapidly degraded to the stable abradcd" condition by manual or mechanical handling. with simultaneous substantial decrease in strength. This is because the initial strength of the fibre. in the low diameter range contemplated. is determined prior to alkali attack primarily by the surface condition of the fibre. In the case of glass fibres of diameter in the range 0.5-1.0 X l0" inches and of oxide composition 19% CaO. 21% A1 0 557: SiO 5% MgO. a virgin" strength when freshly drawn of around 400.000500.000 lbs/sq. in. corresponds to an abraded" strength around 200.000 lbs/sqin.

The glasses used for the purposes of this invention are preferably those capable of fiberization under conditions which are acceptable and convenient on the scale of commercial manufacture. Common methods of fiberization are continuous pulling (or spinning). blowing and centrifugation. The viscosity-temperature relationships of the glasses in the anorthitc field are such as to enable fibres to be conveniently made by pulling in particular. Pulling of fibres is in general much facilitated by including in the glass composition in any event a minor amount of a lluxing agent. The fluxing agent can both reduce the melting point of the glass and the viscosity of the melt, so providing a considerable advantage in the commercial manufacture of the fibres. A preferred fluxing agent is CaF, but other fluxing agents already known for other glasses can be employed. for example P 0 alkali metal oxides and MnO. Mixtures of fluxing agents may also be employed. It is noteworthy that MnO is effective as a fluxing agent as well as being a desirable optional substitueat for the provision in the glass of the desired alkaliresisting properties. The quantities of fluxing agent or agents to be included in the glass depends on the composition of the glass to be drawn into fibres its re fractoriness and its viscosity-temperature relationship. It may be up to I07: by weight of the overall oxide mix of the glass, although usually less. For CaF in some of the glasses studied, a suitable quantity is 3% by weight of the total mix, but significant improvement in pulling characteristics can still be achieved with the incorporation of much smaller percentages.

As compared with products comprising fibres of the glasses mentioned by specific composition above. products ofimproved properties are obtained ifuse is made of fibres derived from certain siliceous glasses containing relatively high proportions of ZrO as described in US. application Ser. No. 748.645. The glasses may also contain minor proportions of other oxides. e.g. Al O;,. capable of substituting for SiO in the network. but SiO- is the dominant glass'forming ingredient. Thus the glass preferably contains as essential ingredient at least 657: SiO and at least 107! Zr() and generally 6571-)? SiO- l020'/r ZrO The percentage ofZrO is preferably about l5 /r to about in /1. In order to ease glass melting and subsequent fiberization it is desirable to add other oxides. network modifiers. in suitable quantities. Alkali and alkaline earth metal oxides and ZnO are amongst the oxides which can be used to mod ify the glass structure in this way. Up to 20% Na O has been found adequate although the preferred proportion is somewhat lower. say l-l2fi. Generally. the network modifier or ntodifiers will be present in the range of 10-20%.

Small quantities of other auxiliary oxides whose precise role in the siliea-zirconia glass structure is not known can nevertheless affect its properties in a favourable way for the production of fibres. Less than 37: of La- O. has been found adequate to reduce the viscosity of the present glasses without increasing their tendency to crystallization.

The network modifiers. and auxiliary oxides. may also act as fluxing agents; Li O for example, acts both as a network modifier and fluxing agent. Fluxing agents which are not also network modifiers will normally be present. however. in a maximum of I092.

A glass containing about 16% ZrO 1V7: Na 0. l7: Li O. l7( Al O remainder (7l7r) SiO is capable of being fiberized at l450l500C to provide alkalircsistant glass fibres suitable for the purposes mentioned herein. It is most surprising that these glasses are capable of being fiberized on a commercially practicable scale bearing in mind the natures of ZrO and SiO;. In addition to the limitation imposed by the l774C melting point of platinum, the metal normally used for bushings when making the glass fibres by spinning techniqucs. the melt requires to have a suitable viscosity and crystallization has to be avoided. These three factors of melt temperature. viscosity and crystallization are to some extent conflicting. A lower viscosity. whilst assisting drawing. increases the risk of crystallization since diffusion of the seed nuclei is accelerated, ZrO is recognized as increasing the refractoriness of the glass. on account of the high melting point of the oxide. and SiO as providing a component in the melt of high viscosity. While SiO ZrO represent the essential oxides of the glasses for the present fibres. other oxides will therefore usually be added as discussed above.

It has also been found that improved fibres and fibre/ccment composites can be derived from certain siliceous glasses containing substantial proportions of SnO Also in accordance with this invention improved glasses. glass fibres. and composite fibre/cementitious products in which the glass fibres are distributed throughout a cement matrix. are those in which the glass comprises SiO as the dominant glass forming ingrcdicnt. an alkali metal oxide or alkaline earth metal oxide or ZnO as the network modifier. and more than 7r by weight of SnO Preferably for-the production of composites of outstanding strength and durability. the glass contains at least 8% SnO ln practice convenient tin oxide glass compositions are those containing at least 557r SiO and a network modifier which is preferably Na O. but may altcrna tively be K 0 or CaO or mixtures of these three oxides. For example. glasses containing 55-8071 SiO- l0307r Na O and 8-1871 SnO- and preferably 70-8071 SiO l0l4'if Na o and 10- l 6% SnO- give rise to very satisfactory materials If desired the tin oxide glasses may contain one or more additional oxides as a flux or partial replacement ofthc glass forming ingredient or network modifier. the

6 total amount of additional oxide or oxides being not greater than I07 and preferably not greater than For example. the SiO- may be replaced to a minor ex tent by Al O In order to ease melting and subsequent fiberizalion fluxing oxides may also be included. in amounts in the range of 1-1071 of the total weight of the other components of the oxide mix. Li O and La O are examples of two such oxides. being used preferably in amounts in the range of 1-30.

The glass fibres contemplated herein have such a high degree of resistance to alkali. as defined above. that the surfaces thereof need not be coated with a water-insoluble coating of the type proposed by Shannon in US. Pat. No. 2.793.l30 to keep the surfaces from contact with the cementitious materials. Furthermore. it is contemplated that conventional materials (sizes) used for sizing or coating glass fibres can be used. Generally. such are employed as an aid in the handling of glass fibres. When contacted with a water/cement slurry and as described reinforced cemcntitious prod ucts are formed. a substantial portion of the size is often unavoidably removed from the glass fibres. thus bringing fibre surfaces into direct contact with the corrosive environment of the slurry. Conventional sizes which can be employed are for example those based on polyvinyl acetate containing. if desired. a silane addi tive and a wetting agent.

Desirably. alkali-resistant glass fibres constitute the sole or at least a major component of the total fibrous reinforcement material in composites according to this invention. However. the use of other fibrous materials providing reinforcement supplementary to that of the glass fibres is not excluded. especially fibres of an artificial nature such as. for example. carbon fibres; usually the supplementary fibres will be present in lesser amount than the glass fibres although the use ofcomparablc quantities. and sometimes equivalent amounts weight for weight. may be recommended for certain kinds of composite products. Chopped or other fibrous forms of glass may be used eg glass wool.

Examples of suitable glass fibres and products made therefrom will now be described.

EXAMPLE 1 Classes of composition as set out in the accompanying Table l were pulled into single filaments with diam eters in range 0.4l.0 X 10 inchcs. and initial "abraded" strengths in the region of from 150.000 400.000 lbs/sq. in. They were then tested for alkaliresistance according to the method previously describcd. with the results given in the Table.

The Table also provides by way of comparison corresponding results obtained for a filament of a standard low alkali borosilicate glass known in the trade under the name E-glass. and containing 8'7? B 0 The results of this Table indicate that the glass fibres are particularly suitable for reinforcing Portland ce ment structures. and are substantially superior in this respect to fibres of E-glass.

EXAMPLE 2 Glass similar to those in Table l but containing a much higher proportion of MnO is also suitable as rein forcing fibres. The performance of a glass fibre made front typical compositions of this family is shown in Table 2.

'lXABLli l Analyns of the ra mix .'\ll\ali-rcs1\lan1;c (ilass (a SiO A1 0. Mgf) 'l'iU M110 (ah 2 reduction Tensile strength Tenslle strength No. in tllamctcr al'ter 10st before test (lbs sq in tlhslstt in.)

l I) 55 2| Nil [30.000 155.000 2 I5 56 2| 5 3 4 [20.000 100.000 3 lb 55 i7 5 5 7.5 lill).(ll|ll 2551") 4 Ii) 60 l5 5 5 5 Nil IUtLUlIU l7ti.(|ll() 5 i5 55 l5 3 h (1 Nil 150.0"0 430.000

E '4 7ll.l)llll 2501100 TABLE 2 Analysis of the glass Alkali-resistance Glass CaO SiO: All) MgO M110 "i reduction in Tensile strength after Tensile strength No. diameter test libs/sq. in.) before lest (lbs/sq. in]

6 l7.0 54.5 ll.5 7.2 9.8 3 l75.000 5.000

In a preferred way of making fibre-reinforced cement In further comparison. asbestos-cement boards of A based composites. a high water/solid ratio is used iniinch thickness and containing 10-1571 asbestos gave an tially for uniform dispersion of fibres and the excess ultimate flexural strength of 4000 lbsfsqin.

water is removed by suction followed by pressing. It should he noted that no attempt was made to opti- Complicatcd shapes can be made by spray mixing of misc the fibre content of composites in Table 3 to yield cement slurry and glass fibre on the surface of perfothe highest possible flcxural strength; also. the rated moulds connected to a vacuum pump. strengths given in Table 3 are average values only and Composites measuring 4 inches X 1 inch X l/4 inch do not reflect the wide scatter observed in the tests.

TABLE 3 Glass After 7 days After 28 days After 90 days After 7 days in After 7 days in No. in water in water in water water and 2\ days water and 83 days in air in air 1 0.000 4.900 5.000 0.550 4.1100 5.2190 5.200 5.030 5.200 4.x10 E-Glass 4.470 4.350 3.030 4.050 3.300

have been made by this method using single-filament In composites made with single filament glass fibre it uncoatcd fibres derived from some of the glasses rcis difficult to avoid unevcn dispersion of the fibres in fcrrcd to in the above Examples and Portland cement. the mix; hence the wide variation in results.

The ro ortion of glass fibre in the composites was 0.5

gm. if g iass to approximately 30 grns. of cement. The EXAMPLE 3 initial water/cement ratio in the slurry was 0.8. which A glass of composition as set out in the accompanyfcll to 0.3 after suction. Glass fibres measuring 4 inches ing Table 4 Glass No. l was pulled into single filaments in length were placed by hand in the tension zone of with a diameter in the range 0.440 X 10 inches. A

these composites during casting. A perforated mould filament was tested for alkali-resistance according to was used and the excess water removed by suction. the method previously described when using Ca (OH) After demoulding. the composite test specimens were as alkali. in comparison with a similar filament of a stored in a constant temperature (64F). constant hustandard low alkali horosilicate glass known under the midity (907: RH.) room. Different curing conditions name E-glass, with the results given in the table.

TABLE 4 Glass No. Anahsis of the Raw Mix Alkali resistance Sit): M103 ZrO. Na O |.i,() 71 reduction tensile tensile in diameter strength strength after before test test 1 71.0 1.0 In 0 11 0 1.0 Nil 190.000 210.000 1-1 9 70.000 255.000

were used and the flcxural strength of the test specimens were determined at different ages. Results are Results are given in Table 5 for the resistance exhibgiven in Table 3 for a typical alkali-resistant glass. the ited at C by filaments of Glass 1 and E-Glass using glass No. in Table l. in comparison with the previas alkali in the test previously described with an alkali ously mentioned Bglass. The values given are for llcxmetal hydroxide. a cement effluent solution of the ural strengths in terms of lbs/sqin. composition specified hereinbcforc.

TABLE 5 Glass Diamelcr of No. fibre before lensile strength lib/in) lest (insl Before test After 24 hr After 48 hr After 72 hr l 0.45 X l' 5.000 340.000 265.000 lltlLlltltl F. 0.48 X l0" 425,000 IHLUUU 40.000 40,000

The strength values of the two glass fibres before test as listed in this table are higher than those in Table 4. This is due to the fact that the fibres were tested in this case soon after they were pulled and did not have the chance to reach their "abraded strength, which is always substantially lower than the virgin strength as pre viously described.

The diameter of the fibre glass No. I remained unchanged after the tests. E-glass fibres were so badly attacked in the test that their diameters could not be measured very accurately afterwards. However. in each case they were found to be definitely smaller than those of the fibres before the test.

In calculating tensile strength of E-glass fibres at all ages after the test, it has been assumed that the diameter remained the same as before the test.

Table 6 provides comparable alkali-resistance test results in the instance when the alkali employed is N NaOH as described above.

TABLE 6 Alkali resistance LII TABLE 8 Glass No. 7 days 28 days in 90 days in in water water at 50C water at 50C Long term results on flexural strengths. again in terms oflbs/sq. in. of composites made with Glass No. l fibres are set out in Table 9.

Glass No. "/1 reduction tensile strength tensile strength in diameter after test before test TABLE 9 l 5 135.000 2l0.000 ln water In air Ii 59 260.000 255.000 after first 7 days in water 180 days 365 days 180 days 365 days 5370 psi 4360 psi 5400 psi 4680 psi It will be noted that the apparent increase in strength due to NaOH attack in the case of E-glass is due to the very large reduction of the diameter of the fibres. If the attack progresses as vigorously as is indicated by this test. there would shortly be no glass fibre left at all to reinforce the cementitious matrix.

The result of Tables 4. 5 and 6 indicate that fibres of the glass are particularly advantageous for reinforcing Portland cement structures. Further tests have shown that at this temperature (80C) fibres products from Glass No. l when kept immersed in the "cement effluent" solution for a period of two weeks still retain some measurable tensile strength. After 96 hours exposure. the E-glass fibres could not be tested.

Results are given in Tables 7 and 8 for the flexural strengths of Portland cement composites reinforced by fibres of Glass No. 1 (two sets of results) in comparison with strengths for composites reinforced by fibres of E-glass, The values given are for flexural strengths in terms of lhs/sqin. Manufacture of the composites and the test conditions were carried out as described in my earlier US. Pat. application No. 649.463.

(average of 6] (average of 3) (average of (1] (average of 3) These values refer to the second series of values given for Glass No. l in Table 7. The values given in Table 7 are averages of nine results and cannot be compared. in the strictest sense. with the present results. Although a drop in strength is noted after one year. these results are vastly superior to those obtainable with E-glass fibres.

It should be noted that no attempt was made to optimisc the fibre content of composites in Tables 7. 8 to yield the highest possible flexural strength; also. the strengths given in Table 7 are average values only and do not reflect the wide scatter observed in the tests. In composites made with single filament glass fibre it is difficult to avoid uneven dispersion of the fibres in the mix; hence the wide variation in results.

EXAMPLE 4 Glasses of composition given in Table l0 were used. The amount of fluxing agent is expressed as a percentage of the total SiO- Na O. SnO combined weight.

l 1 12 The glasses were pulled into single filaments with a di- TABLE 1 ameter in the range 0.4-0.5 X inches. and a filament of each glass was tested for alkaliresistance ac- Curdmg to mclhod previously described using (ilass Tensile strength Reduction in diameter (OH )3 as alkali. The results are given in Table l l. 1W "W100 1' Results are given in Table l2 for the resistance exhib 1 35mm" ited at 80C by filaments in the test previously de- 3 3 scribed using. instead of an alkali metal hydroxide. the typical cement effluent" solution of composition 5 230.000 1 0 given hercinbefure. m

Table 13 provides a comparable alkali-resistance test TABLE I2 Cement Effluent Tesl (iluss Tensile strength after Reduction in diameter No. 1 wk. 2 wks. 4 wks 24 wks. after 1 weeks ('1' 1 results for filaments when the alkali employed is N TABLE 3 NaOH as described above. The filaments again had di- 25 ameters in the range of 0.4-0.5 l0" inches.

ln these TABLES. the quotes tensile strength values 0 1 m. lrungth Rcduuilm in dimer." were obtained using apparatus described in Current Paper No. 26/68 (March 1968) issued by the Building 1 320000 x 6 Research Station. Bucknalls Lane. Garston, Watford. 30 a Hertfordshire. under the title Apparatus for testing 2; 5 1 :5 tensile strengths of corroded glass fibres" (R. S. Gillett 5 210.000 3 A 4 and A. .l. Majumdar). Composites measuring 4 inches X l inch X [1 inch have been made using single-filament TABLE I4 PORTLAND CEMENT COMPOSITE STRENGTHS (modulus of rupture in lbs/inf) Glass After 7 days After 28 days After 90 days After 0 months After 1 year No. in water in in in in water air water air water air water air I 5720 H00 6750 6440 M50 bl 10 6750 S050 6000 d ib s driv d from the tin oxide lasses of uncoatc f rc L e g EXAMPLE 5 Table ID by the same method as described in Example 2.

Results are given in Table I4 for the flexural strengths of Portland cement composites reinforced by fibres of Glass No. l. The values given are for flexural strengths in terms of lbs/sq.in. Manufacture of the composites and the test conditions were carried out as described in my U.S. Pat. application Nos. 649.463 and 748.645.

TABLE 10 Glass Fibre Compositions l3 filaments ll-l3 am in diameter. Both types of glass fibres had a polyvinyl acetate coating on them.

In this method. cement slurry having a high water/dry pact. The flexural and tensile strengths were determined using an Instron testing machine whereas for measuring the impact strength of the material an lzod cement ratio (404071) and glass-fibre rovings type instrument having a capacity of l2 Joules was emchopped in situ to the desired lengths were sprayed si- 5 ployed. The results are shown in Table 15.

TABLE I5 L'UMPOSlTF. Tl-NSILI: Fit-RURAL IMPACT STRENGTH STRENGTH STRENGTH (P.S.l.) (P.S.l.l (inch-lblsqin.) 28 days i year 28 days I year 13 days I year E-glass 2650 Hill) (1630 27m 15 is Storage condltmns (a) Glass No. l 1530 2H0 soon 5304) m5 I30 li-glass 6630* 57m 165 110 Storage conditions lb) (ilitsh No i 2430 2260 M150 5900 130 I3 'v-atehcured multaneously on to a paper-covered. perforated metal face ofa suction mould. Spraying was continued until a 1 claim: thickness of 10 to l3 mm was attained. The top surface 1. An alkali-resistant glass fibre derived from a glass was then levelled off and the excess water extracted by consisting essentially of. in percent by weight, 658()7r the application of suction. The quantity of Glass No. l SiO,,. l()-'7r ZrO and lO2O71 of at least one netfibres used was 5% by weight of the wet board at this work modifier which is an alkali metal oxide, an alkastage whereas with E-glass 6% by weight was used. lmline earth metal oxide. or ZnO. said glass being one mediately after this the composite boards were rcwhich has a tensile strength of at least 100,000 pounds moved from the mould. cut into 150 mm X l m strips per square inch as determined after contacting a fibre with a knife. covered with polythene sheets and stored having a diameter from 0.4 to l.() X It) inch and a under laboratory conditions for 7 days. When the length ofZVz inches with a saturated Ca (OH) solution boards had hardened sufficiently. they were sawn into for 4 hours at l0OC.. removing the fibre from the solusmall l5() mm X 50 mm specimens and after 7 days tion and washing the fibre in sequence with a dilute sostorage in the moist environment. the specimens were lution of aqueous HCl. water. and acetone, and drying, randomly selected and were placed under different curthe fibre experiencing not more than 10% reduction in ing conditions. In the case of the board made with the diameter during said test. alkali resistant fibre, a portion of the board measuring 2. A fibre according to claim I. wherein the glass l m X l m was left uncut and this was removed to a 90 contains up to 10% by weight of at least one fluxing percent humidity room for storage subsequent to the agent selected from the group consisting of CaF P 0 initial 7-day moist curing. and MnO.

In general. three conditions of storage were used: (a) 3. A fibre according to claim 1, containing Na- O and under water at l8C. (b) in air of 407: RH at l8C and Li O. (c) natural weatherings. Specimens subjected to natu- 4. A fibre according to claim I. wherein the ZrO, ral wcatherings were kept in a horizontal position well content of the glass is l5l67( by weight. above the ground on a wooden frame placed on the ex- 5. A fibre according to claim 1, wherein the glass posure site. contains about 7l% SiO,. 16% 210 H7: Na O, 1%

For each type of GRC composite material stored Li O. l% A1 0 under the environmental conditions mentioned above. 6. A fibre according to claim 1, wherein the network tests were carried out to determine the flexural modifier is an alkali metal oxide. strength. the tensile strength and the resistance to im- 

1. AN ALKALI-RESISTANT GLASS FIBRE DERIVED FROM A GLASS CONSISTING ESSENTIALLY OF, IN PERCENT BY WEIGHT, 65-80% SIO2, 10-20% ZRO2, AND 10-20% OF AT LEAST ONE NETWORK MODIFIER WHICH IS AN ALKALI METAL OXIDE, AN ALKALINE EARTH METAL OXIDE, OR ZNO, SAID GLASS BEING ONE WHICH HAS A TENSILE STRENGTH OF AT LEAST 100,000 POUNDS PER SQUARE INCH AS DETERMINED AFTER CONTACTING A FIBRE HAVING A DIAMETER FROM 0.4 TO 1 .0 X 10**-3 INCH AND A LENGHT OF 2 1/2 INCHES WITH A SATURATED CA (OH)2 SOLUTION FOR 4 HOURS AT 100*C., REMOVING THE FIBRE FROM THE SOLUTION AND WASHING THE FIBRE IN SEQUENCE WITH A DILUTE SOLUTION OF AQUEOUS HC1, WATER, AND ACETONE, AND DRYING, THE FIBRE EXPERIENCING NOT MORE THAN 10* REDUCTION IN DIAMETER DURING SAID TEST.
 2. A fibre according to claim 1, wherein the glass contains up to 10% by weight of at least one fluxing agent selected from the group consisting of CaF2, P2O5 and MnO.
 3. A fibre according to claim 1, containing Na2O and Li2O.
 4. A fibre according to claim 1, wherein the ZrO2 content of the glass is 15-16% by weight.
 5. A fibre according to claim 1, wherein the glass contains about 71% SiO2, 16% ZrO2, 11% Na2O, 1% Li2O, 1% Al2O3.
 6. A fibre according to claim 1, wherein the network modifier is an alkali metal oxide. 